Currently, permanently-implanted pacemakers (PPMs) utilize one or more electrically-conductive leads (which traverse blood vessels and heart chambers) in order to connect a canister with electronics and a power source (the can) to electrodes affixed to the heart for the purpose of electrically exciting cardiac tissue (pacing) and measuring myocardial electrical activity (sensing). The leads may experience certain limitations, such as incidences of venous stenosis or thrombosis, device-related endocarditis, lead perforation of the tricuspid valve and concomitant tricuspid stenosis; lacerations of the right atrium, superior vena cava, and innominate vein or pulmonary embolization of electrode fragments during lead extraction.
A small sized PPM device has been proposed with leads permanently projecting through the tricuspid valve and that mitigate the aforementioned complications. Optionally, an entire PPM with lead may be in atrium only and not have a lead projecting through the tricuspid valve. The PPM is a reduced-size device, termed a leadless implantable medical device (LIMD), characterized by the following features: electrodes are affixed directly to the can of the device; the entire device is attached to the heart.
The LIMD are able to sense in one or two chambers and deliver pacing pulses in the same chambers. For example, an LIMD may be located in the right atrium to offer various mode functionality. An AAI mode LIMD typically only senses in the right atrium, paces in the right atrium, and inhibits pacing function when an intrinsic event is detected in the right atrium within a preset time limit. Similarly, an LIMD may be located in the right ventricle to offer various mode functionality. A WI mode LIMD typically only senses in the right ventricle, paces in the right ventricle, and inhibits pacing function when an intrinsic event is detected in the right ventricle within a preset time limit.
Optionally, a DDD mode LIMD may be located in the right atrium or right ventricle. The DDD mode LIMD may include a stabilizing intra-cardiac (IC) device extension that has an electrode provided thereon. The LIMD with the IC device extension collectively provide pacing and sensing in the RA and RV and inhibit pacing when an intrinsic event is detected.
However, the LIMDs proposed thus far exhibit certain limitations. For example, LIMDs include multiple components within the housing that limit the degree to which cost and size can be reduced. For example, LIMDs include an electronics module, battery and multiple feed-thrus within the housing. The feed-thrus afford interfaces for conductors to leave and enter a hermetically sealed chamber or area within the LIMD. As one example, LIMDs utilize a feed-thru between the interior of the housing and the leads that carry at least one electrode to pace/sense in the RA. LIMDs utilize another feed-thru between the battery and the electronics module. The use of multiple feed-thrus increases the cost and size of the LIMD. A need remains or an LIMD design that utilizes fewer feed-thrus and decreases the size and cost of the LIMD.